I'm working on a little system plugin to inject Facebook Open Graph properties into an article. Therefore I've been using $document->setMetaData(). But now I discovered that this adds <meta name=""> tags to the header of the page, but Facebook expects <meta property=""> tags.

What's the easiest way to put a <meta property=""> tag into the page header?

Please explain in as much detail as possible, as I'm absolutely new to Joomla plugin developemnt.